The present invention relates to an improved current-conducting arm for an electric arc furnace, and more specifically, to a design for a current-conducting arm that efficiently conducts current to an electrode being held by the current-conducting arm and that may be assembled and maintained in a simple manner.
It is reported that electric arc furnaces produce roughly two-fifths of the steel that is made in the United States. Generally, electric arc furnaces comprise a heating chamber that uses electricity conducted through a current-conducting arm to obtain very high temperatures within the electric arc furnace to melt and alloy metals. Moreover, electric arc furnaces are constructed to purportedly produce almost all the stainless steels, electrical steels, tool steels, and special alloys required by the chemical, automotive, aircraft, machine-tool, transportation, and food-processing industries.
To produce the high temperatures within the furnace, electric arc furnaces use the current-conducting arm to transmit a current to an electrode, which will then generate an arc to melt the desired metal within the furnace by supplying energy to the furnace interior. Electrical energy is supplied from the current-conducting arm to at least one electrode, and the electrode supplies energy to the metal. The purpose of a current-conducting arm is to conduct electrical current from a set of cable connection points to the graphite electrode. As a result, it is important to have the most efficient means available to provide an electric current to the electrode held by the current-conducting arm.
Conventional current-conducting arms (as illustrated in FIG. 1) include a rectangular arm housing 100, an electrode-clamping band 102 or electrode holder, a spring mounted within the arm housing that engages the electrode-clamping band 102, a cylinder mounted within the arm housing, and a series of water cooling pipes that are also mounted within the arm housing to control the temperature within the current-conducting arm. The arm housing of a conventional current-conducting arm is created by welding four rectangular metal plates 104 together at the edge of each plate such that the housing has a rectangular cross-section, as illustrated in FIG. 2. This welded arrangement of the arm housing creates a problem in that there is a high concentration of current in the rectangular corners where the plates 104 are connected together, whereas the remaining surface area of each plate of the arm housing has lower current concentration. In an attempt to solve this problem of high current concentration in the rectangular corners, prior designs applied copper to the corners of the current-conducting arm to aid in the conduction of the current. Nevertheless, in some cases, the current concentration in the corners was so significant in the corners such arms that the copper was stripped from of the corners of the current-conducting arm.
Moreover, each of the weld seams 106 where the plates are welded together provides areas of increased resistance to the conduction of current. Consequently, the current is not conducted through this conventional arm to the electrode with the efficiency that is desired, which will further diminish the efficiency of the melting of the material contained in the furnace.
In addition, the large size of all traditional current-conducting arms provides a problem in the mounting and maintenance of the current-conducting arms in an electric arc furnace. First, improperly aligned current-conducting arms can cause problems with respect to the operation of the electric arc furnace as well as the electrode held by the current-conducting arm. For example, unaligned current-conducting arms can create a weakness in the electrode held by the current-conducting arm. This weakness in the current-conducting arm can further lead to premature deterioration and failure of the electrode held by the current-conducting arm, which requires early replacement of the electrode in the electric arc furnace.
Additionally, conventional current-conducting arms include several components that provide a secure connection for the electrode being held. Such conventional elements include the spring that is connected to a hydraulic cylinder inside the arm to maintain the position of the electrode. The conventional spring is used to pull the electrode towards the arm, with the length of the spring being designed so that the force required to securely engage the electrode is applied. A problem with such a design is that if either the spring or the hydraulic cylinder experiences failure, then the conventional current-conducting arm must be disassembled so that maintenance can be provided for each of the inoperable elements within the current-conducting arm.
What is desired, then, and not found in the prior art, is a current-conducting arm having a design that provides efficient transmission of electrical current, that provides an efficient means for building the arm, and that further reduces maintenance time required to maintain the operability of the arm.
An object of the present invention is to provide a current-conducting arm for an electric arc furnace having a design promoting the efficient conduction of electric current to an electrode.
A further object of the present invention is to provide a current-conducting arm for an electric arc furnace having an arm housing that may be assembled in a simple fashion along two weld seam lines.
Another object of the present invention is to provide a current-conducting arm for an electric arc furnace that may be maintained in a simple fashion.
An additional object of the present invention is to reduce the area within the arm occupied by a spring that maintains the position of the electrode.
A further object of the present invention is to provide a current-conducting arm for an electric arc furnace that provides a means for precisely mounting the current-conducting arm in the electric arc furnace.
The current-conducting arm of the present invention is designed to hold an electrode within an electric arc furnace. The current-conducting arm of the present invention includes an arm housing that surrounds and protects the various other components of the current-conducting arm, and that is furthermore used to distribute electric current to the electrode. The arm housing includes a base channel member and a top channel member, with both channel members being U-shaped. In assembling the arm housing, the top channel member is inverted such that the edges of the top channel member may be welded to the edges of the base channel member, such that the base channel member is the mirror-image of the top channel member. Consequently, this current-conducting arm may be produced with relative ease, and the design of the arm housing reduces the number of weld seams from conventional current-conducting arms.
The current-conducting arm also includes a spring assembly and a hydraulic cylinder that are encased in the arm housing. The spring assembly includes at least two springs that are positioned between a spring casing and a rear plate. The spring assembly is used to maintain a return force on the electrode to draw the electrode toward the current-conducting arm as with a conventional spring, while reducing the space required inside the arm for the spring assembly. Moreover, the present current-conducting arm includes a spring access cavity that provides convenient access to the spring assembly by the user to reduce the difficulty in maintenance of the current-conducting arm. As a result, the user is able to easily replace the spring assembly as required.
A series of bolt members are also included in the present invention to secure the position of the current-conducting arm with respect to the electric arc furnace. Access to the bolt members is provided through a set of cavities that are provided in the top channel member, which again improves the conditions for maintenance of the arm.
These and other objects and advantages of the invention will become apparent from the following detailed description of the preferred embodiment of the invention